The present disclosure herein relates to the field of preventing or easing cell data corruption of a volatile semiconductor memory, and more particularly, to a memory system for an access concentration decrease management of a specific word line or bit line of a semiconductor memory device and an access concentration decrease method.
A volatile semiconductor memory device such as a dynamic random access memory (DRAM) is being widely used in an electronic device such as a mobile device or a computer as a main memory.
A memory system including a semiconductor memory device and a memory controller may be embedded in or connected to a host device such as a microprocessor.
In a memory system, in the case that the number of times a specific word line or bit line is accessed is far more than that of other word lines or bit lines, data retention reliability of memory cells connected to adjacent word lines of the specific word line or memory cells connected to adjacent bit lines of the specific bit line may be relatively degraded.
For example, in the case that a specific address is concentratedly applied to a semiconductor memory, data stability of memory cells connected to a word line or bit line which the specific address indicates or memory cells adjacent to the memory cells may be degraded. This is because if coupling or well bias is changed in a semiconductor memory such as a DRAM, the quantity of charges charged in a storage capacitor is changed. Data representing 1 or 0 in a semiconductor memory such as a DRAM is determined by the quantity of charges of a storage capacitor constituting a memory cell. As a manufacturing process of DRAM is miniaturized, if an access is concentrated on a specific word line, memory cells connected to adjacent word lines of the specific word line may be disturbed or access transistors connected to the specific word line may be under stress. Thus, data retention time of memory cells is reduced and thereby a refresh characteristic may get worse.
In the DRAM, by request of high speed, high capacity and low power consumption, a space between word lines, a space between bit lines and a space between memory cells are increasingly being reduced.
Thus, when memory cells connected to any word line are accessed, memory cells connected to word lines adjacent to the word line being accessed suffer spatial disturbance due to a coupling effect. In the case that an access to a specific word line concentratedly occurs, cell data stored in memory cells connected to the adjacent word lines are liable to corruption. For instance, a memory cell storing data “1” may be read as “0” or a memory cell storing data “0” may be read as “1”.
If corruption of cell data occurs due to a concentration access to a specific word line or a specific memory area, a critical error of a data storage device may occur.
There may be an increase in a dynamic coupling occurring when an access concentratedly performed to a specific word line and an increase in interference due to an electric field as reasons that a refresh characteristic is degraded due to degradation of retention characteristic.
In a DRAM, in the case that a normal word line is tested to be failed and is repaired by a spare word line, it is necessary to care adjacent spare word lines physically adjacent to the spare word line.
However, since the failed normal word line is randomly or flexibly replaced with one of a plurality of spare word lines, it is difficult to accurately obtain addresses of spare word lines physically adjacent the spare word line.